The story takes place in the Borough (Aldeburgh) early in the 19th century.
Prologue: Interior of the town hall.
An inquest is underway to determine the cause of death of a boy apprenticed to the fisherman Peter Grimes. The mayor, Swallow, rules the death accidental, but warns Grimes not to hire another apprentice. The fisherman angrily rejects that injunction and complains that the verdict will not dispel the ill feelings the townspeople harbor toward him. Of those present, only Ellen Orford, a school teacher, displays any sympathy for Grimes.
Interlude I: "Dawn"
Act I, Scene 1: A street by the shore, a few days later.
The townsfolk are busy at their daily work. Grimes calls for help hauling his boat ashore, but only Balstrode, a retired seaman, and Ned Keene, an apothecary, come to his aid. Keene tells Grimes of a workhouse boy he could take on as a new apprentice. Hobson, the carter, refuses to fetch the lad, but Ellen volunteers to bring him. After she departs, a storm arises. The townsfolk seek shelter, leaving Grimes and Balstrode alone. Balstrode advises the fisherman to leave town and go to sea, but Grimes declares that he is rooted to the place. He also confesses his dream of a prosperous life and marrying Ellen.
Interlude II: "Storm"
Act 1, Scene 2: That evening, inside the Boar, a tavern.
As the townsfolk take shelter from the storm, Grimes arrives, soaked and wild in appearance. He likens the storm to the turmoil of human affairs, provoking derision and hostility. Auntie, the tavern's mistress, tries to relieve the tension by instigating a song. Just then, Ellen and the new apprentice arrive, drenched and exhausted. Dispensing with any pleasantries, Grimes hustles the boy out and repairs toward his hut.
Interlude III: "Sunday Morning"
Act II, Scene 1: The street again, on a fine Sunday morning several weeks later.
Ellen and the new apprentice sit in the sun by the shore while a service is conducted in the parish church. Noticing the boy's torn clothes and bruised neck, she confronts Grimes when he comes for his apprentice. Ellen and Grimes quarrel, and he strikes her. The townsfolk gather and voice their anger at Grimes until the Rector and Mayor Swallow lead the men toward the fisherman's home.
Interlude IV: "Passacaglia"
Act II, Scene 2: Inside Grimes's hut.
Grimes, eager to reach a large shoal of fish, roughly orders his apprentice about. When his behavior frightens the boy, Grimes tries to calm him by telling how well they will live if they make a good haul and he marries Ellen. In spite of himself, he knocks the boy over, then comforts him again, his demeanor swinging wildly between roughness and tenderness. Grimes hears the townsmen approaching. Anxious to be off, he pushes his apprentice out the door, and the boy slips and falls off the cliff to his death. Grimes scrambles down after him. The townsmen arrive and are surprised to find the hut empty. All depart except Balstrode, who looks about and then heads for the path that leads down the cliff.
Interlude V: "Moonlight"
Act III, Scene 1: The street again, several days later.
The townsfolk are gathered for a dance. Ellen tells Balstrode that Grimes's boat has returned, but that the jacket his apprentice was wearing has washed up on the beach. This news is overheard and passed on to Mayor Swallow, who orders a party to find Grimes.
Act III, Scene 2: A few hours later.
In the fog that has set in, the townsmen search for Grimes. Ellen and Balstrode intercept the fisherman as he attempts to return home. He is exhausted and mad with grief and desperation. Balstrode tells Grimes the only way out of his predicament: to take his boat back out to sea and scuttle it. Dawn breaks, and the townsfolk resume their routines. Swallow relates that a boat was seen on the horizon, apparently sinking. His report is dismissed as rumor, and the people return to their business.